Fourth Excited State Research Articles

Two-dimensional self-consistent microwave argon plasma simulations with experimental verification

Optical emission spectroscopy (OES), absorption measurements, and thermal energy rate analysis were used in tandem with numerical models to characterize microwave argon plasmas. A WAVEMAT (model MPDR-3135) microwave diamond deposition system was used to generate argon plasmas at 5 Torr. Three excited state number densities (4p, 5p, and 5d) were obtained from the OES measurements, and a fourth excited state number density (4s) was obtained from the absorption measurements. Further, power absorbed in the substrate was monitored. A self-consistent two-dimensional argon model coupled with an electromagnetic field model and a 25-level two-dimensional (2D)-collisional-radiative model (CRM) was developed and validated with the experimental measurements. The 2D model provides the gas and electron temperature distributions, and the electron, ion, and 4s state number densities, which are then iteratively fed into the electromagnetic and CRM models. Both the numerically predicted thermal energy rates and excited state densities agreed, within the experimental and numerical uncertainties, with the experimental results.

Nucleon electromagnetic structure revisited

Unitary and analytic ten-resonance model of the nucleon electromagnetic (e.m.) structure with canonical normalizations and QCD (up to the logarithmic correction) asymptotics is constructed on the four-sheeted Riemann surface, which provides a superposition of vector–meson pole and continuum contributions in a very natural way. As a result it describes simultaneously all existing experimental space-like and time-like data on the proton e.m. form factors (ff's) and on the neutron e.m. ff's as well. A crucial factor in the latter achievement is the inclusion of a contribution of the fourth excited state of the ρ(770) meson with the parameters mρ′′′′ = 2455 ± 53 MeV, Γρ′′′′ = 728 ± 2 MeV and (f(1)ρ′′′′NN/fρ′′′′) = 0.0549 ± 0.0005, (f(2)ρ′′′′NN/fρ′′′′) = −0.0103 ± 0.0001. The pronounced effect of the two-pion continuum on the isovector spectral functions demonstrating a strong enhancement of the left wing of the ρ(770) resonance close to two-pion threshold, which was revealed by Höhler and Pietarinen by means of the nucleon ff unitarity condition more than a quarter of the century ago, is predicted by the model automatically. The model gives large values of the f(1,2)ϕNN coupling constants, thus indicating the violation of the OZI rule. Since in the framework of the considered model isoscalar ff's above their lowest branch point ts0 = 9m2π are complex functions, the isoscalar spectral function behaviours are predicted as well.

Internal axis molecular parameters, torsional energies and matrix elements of methyl mercaptan-D 2

In this paper an internal axis method Hamiltonian model has been applied to evaluate the torsional–rotational molecular parameters of asymmetrically substituted methyl mercaptan (CHD 2SH) using previously observed microwave transitions. The torsional potential barrier function V 2 has been obtained. The pure torsional energies and matrix elements between various torsional sub-levels up to the fourth excited torsional state in the ground vibrational state have been determined. The matrix elements and the torsional energies will be of great value to researchers seeking the spectrum of this molecule.

Widely tunable self-assembled quantum dot lasers

Quantum dot laser diodes with up to five well-defined electronic shells are fabricated using self-assembled quantum dots (QDs) grown by molecular beam epitaxy. At 77 K, we tune the lasers from the first to the fourth excited state of the QDs by varying the cavity length, this covers a wavelength range from 869 to 963 nm. At room temperature, we obtain lasing from the second to the fourth excited state covering the 938 to 984 nm wavelength range. For high injection currents, a large part of the QD ensemble contributes at once to the stimulated emission yielding a lasing emission linewidth having a full width at half maximum of 25 nm. By increasing the energy spacing between the QD energy level contributing to the lasing and the wetting layer energy levels, improved thresholds at higher temperatures are observed, leading to lasing below 100 A/cm2 at room temperature.

Torsional energies, matrix elements and predictions of microwave transitions in CH2DOD

In this study the torsional–rotational molecular parameters of asymmetrically deuterated methanol (CH2DOD) have been calculated up to K=15 in the torsional vibrational ground state. Matrix elements for ΔK=±1 transitions have been calculated up to the fourth excited torsional state. Using previously observed microwave (MW) transitions effective state dependent molecular parameters have been evaluated for the states involved. These parameters allow the predictions for unobserved microwave transitions to be made with a precision which should enable future laboratory and astrophysical detection. The matrix elements and the torsional energies will be valuable in the assignments of far-infrared absorption spectra and optically pumped far-infrared laser lines in this molecular isotopomer of methanol. The energy levels calculated will form a useful data-base to aid in the detection of this isotopic variant of methanol in astrophysical sources which might be of useful for the determination of parameters like the D/H ratio in the universe.

Torsional energies and matrix elements for far-infrared absorption transitions in the ground vibrational state of ethyl alcohol

The pure torsional energies and matrix elements for b and c type transitions in the vibrational ground state of ethanol (CH 3CH 2OH), obtained using an internal axis method (IAM) theory are reported. Torsional energies and matrix elements for Δ K=±1 transitions have been calculated up to K=15 and up to the fourth excited torsional state (o 7). The a-type microwave (MW) frequencies for the first excited OH-torsional state (e 2 and o 3) have been fitted with an expansion model and the coefficients determined. These allowed the predictions of several yet unobserved astrophysically important MW transitions. In addition, the leading terms of an effective Hamiltonian have been determined for the e 2 and o 3 sub-levels. The present calculations should prove valuable in the assignments of far-infrared spectra and optically pumped far-infrared laser lines.

Torsional eneÅrgies and relative intensities of far-infrared transitions in the vibrational ground state of methanol-D 2

In this paper, the pure torsional energies of asymmetrically deuterated methanol CHD 2OH have been calculated up to the fourth excited torsional state in the vibrational ground state, using an internal axis method (IAM) Hamiltonian. Relative intensities for all possible strong b- and c- type far-infrared (FIR) transitions for K≤15 in the torsional vibrational ground state have also been reported. Matrix elements for all possible Δ K=±1 transitions have been calculated up to the fourth excited torsional state. The calculations will be useful in the assignments of high resolution far-infrared spectra and optically pumped far-infrared laser lines in this molecular species. The energy levels calculated will provide excellent data base for astrophysical detection in the interstellar space.

Electronic and impurity states in a three-dimensional corner under an applied electric field

We study the electronic and impurity states in a three-dimensional corner under an applied electric field. It is found that the electronic states in the corner are discrete in all three directions, similar to the electronic state behaviour in a quantum dot, and the eigenenergies of the discrete electronic levels increase with the electric field strength. The impurity states in the three-dimensional corner have similar features as those in the quantum dots, and their maximum binding energy increases, but the impurity position corresponding to the peak binding energy moves towards the corner, as the electric field strength increases. The results also show that the binding energy of the ground impurity state at the corner point in the absence of electric field is equal to that of the fourth impurity excited state in the bulk.

Internal axis molecular parameters, torsional energies and matrix elements of methyl mercaptan-D 1

In this paper an internal axis method Hamiltonian model has been applied to evaluate the torsional–rotational molecular parameters of asymmetrically substituted methyl mercaptan (CH 2DSH) using previously observed microwave transitions. The torsional barrier potential barrier functions V 1, V 2 and V 3 have been refined. The observed microwave transition frequencies have also been fitted to an energy expansion model, which allowed accurate predictions of yet unobserved transition frequencies with microwave accuracy. These values are independent of the Hamiltonian model used and will prove valuable for astrophysical detection. The matrix elements between various torsional sub-levels upto the fourth excited torsional state in the ground vibrational state.

Torsional energies, matrix elements and relative intensities of far-infrared absorption transitions in CH 2DOH

In this paper, the relative intensities of far infrared transitions in the torsional ground state of asymmetrically deuterated methanol CH 2DOH are reported, using an internal axis method (IAM) theory. Relative intensities are presented for all possible strong b- and c-type Far Infrared (FIR) transitions upto K = 15 in the torsional vibrational ground state. Matrix elements for Δ K = ± 1 transitions have been calculated upto the fourth excited torsional state. The calculations will be valuable in the assignments of far-infrared spectra and optically pumped far-infrared laser lines. The energy levels calculated will provide excellent data base for astrophysical detection of asymmetrically substituted methanol, which is of significant importance for the determination of parameters like the D H ratio in the universe.

Quantification of fluorine in SiF x etch residues on silicon with proton induced γ-emission

Reactive ion etching of Si wafers with a CF 4 plasma results in the formation of a very thin layer of SiF x . Quantification of the fluorine areal density as a function of plasma parameters is important for models describing the etching process. The Eindhoven AVF cyclotron has been used to quantify the amount of deposited fluorine using the 19F(p,p′γ) 19F reaction detecting the 110 and 197 keV γ-lines with a hyperpure Ge detector. The energy of the proton beam was chosen to be 2.76 MeV thereby limiting the Compton background by suppressing excitation of the fourth excited state ( 5 2 + ) of 29Si. Quantification was obtained through the use of an implantation standard. A detection limit of 1 × 10 14 F/cm 2 was obtained and two series of pilot experiments were carried out in which gas discharge pressure and plasma power density have been varied.

Threshold photoelectron spectroscopy of BCl3 and fragmentation of the valence electronic states of BCl3 +, studied by coincidence spectroscopies

The valence threshold photoelectron spectrum (TPES) of BCl3 is reported for the first time. Threshold photoelectron–photoion coincidence (TPEPICO), photoion-fluorescence coincidence (PIFCO) and threshold photoelectron-fluorescence coincidence (TPEFCO) spectroscopies have also been used to measure for the first time, state selectively, the decay pathways of the valence states of BCl3+ in the range 11–19 eV. Vacuum UV radiation from a synchrotron source dispersed by a 5 m normal-incidence McPherson monochromator ionises the parent molecule, and electrons and ions are detected by threshold electron analysis and time-of-flight mass spectrometry, respectively. Undispersed fluorescence from the interaction region can also be detected, allowing the three different types of coincidence experiment to be performed. There are major differences in the intensity distribution of the different bands in the TPES of BCl3 compared with its He I photoelectron spectrum which we attribute to autoionisation. TPEPICO spectra are recorded continuously as a function of photon energy, allowing yields of the fragment ions to be obtained. Over the range 11–19 eV, only the ions BCl2+ and BCl3+ are observed. The ground electronic state of BCl3+ is stable with respect to dissociation to BCl2+, whereas the five excited electronic states fragment to BCl2++ Cl. Kinetic-energy releases into BCl2++ Cl have been measured at the Franck–Condon maxima of the C 2A″2, D 2E′ and E 2A′1 excited states of BCl3+ with good time resolution. PIFCO and TPEFCO spectra are recorded at fixed photon energies. The former experiment can yield the fate of the lower electronic state of the parent ion to which fluorescence occurs. The latter experiment can yield the lifetime of the fluorescing state. Radiative decay is confirmed to occur from the fourth excited state of BCl3+(D 2E′) at 15.5 eV, and the lifetime of this state is measured to be 5.5 ± 0.5 ns. The absence of parent ion signal in the energy-scanning TPEPICO spectrum through the D state allows us to put an upper limit on the fluorescence quantum yield of this state of ca. 0.04.

Relative photoionization cross section study of OH and OD from 68 nm to 95 nm

The photoionization spectra of OH and OD have been reported from 680 to 950 AA (18.23 to 13.05 eV) at a wavelength resolution of 0.07 AA. Through interpretation of both spectra, the Rydberg series and their higher vibrational members have been reported for three of the excited ionic states, a1 Delta , A3 Pi i, and b1 Sigma +. A vibrational progression has also been observed in both OH and OD which is apparently related to a fourth excited ionic state, c1 Pi . Finally, the dissociative ionization limits, corrected to 0 K, for H2O and D2O have been measured to be 18.11+or-0.01 and 18.21+or-0.01 eV, respectively, and shown to be in good agreement with previously reported results.

Collisional Excitation of O +2 and N +2 Electronic States via Single Electron Capture by B 2+ Ions

High-resolution translational energy spectra have been obtained for single-electron capture by 4-keV B 2+ ions in collision with Ne, O 2, and N 2. The Ne spectrum is used for accurate determination of the zero energy-change position for subsequent analysis of the complex molecular spectra. Six capture channels have been unambiguously identified for the O 2 spectrum; two of these involve capture-excitation, which leaves the O + 2 ion in its fourth excited state, responsible for subsequent emission of the first negative band system [ b 4Σ − g → a 4Π u ] of O + 2. The N 2 spectrum consists of seven narrow spectral features, four of which are identified with capture channels from which the first and second excited electronic states of the N + 2 ion are accessed. These constitute the upper states of the Meinel [ A 2Π u → X 2Σ − g ] and first negative [ B 2Σ + u → X 2Σ + g ] band systems of the N + 2 ion.

Non-yrast states in 125Xe

The non-yrast states of 125Xe have been investigat with the 122Te(α, n) and 123Te(α, 2n) reactions by means of in-beam γ-spectroscopy using a setup of 6 Compton-suppressed high-purity-germanium (HPGe)detectors. Over 400 new transitions establishing over 110 new levels could be placed in a level scheme totalling 196 levels connected by 563 transitions. 77 spin and parity assignments were made (some of them tentatively) and 35 multipolarity mixing ratios could be assigned to transitions using the γ-angular distribution, γ-linear polarization, γγ-DCO-analysis and γ-excitation-function methods. The negativeparity data are compared to the predictions of the rigid-triaxial-rotor-plus-particle model and the interacting-boson-fermion model. Both calculations describe successfully the excitation energies of these non-yrast states. The branching ratios of the lower non-yrast states are also reproduced very well. Only at the fourth and higher excited states of a given spin, a discrepancy between experiment and theory was observed.

Use of threshold electron and fluorescence coincidence techniques to probe the decay dynamics of the valence states of CF+4, SiF+4, SiCl+4, and GeCl+4

Threshold photoelectron–photoion coincidence (TPEPICO), photoion–fluorescence coincidence (PIFCO), and threshold photoelectron–fluorescence coincidence (TPEFCO) spectroscopies have been used to measure, state selectively, the decay pathways of all the valence states of four gas-phase tetrahedral ion CF+4, SiF+4, SiCl+4, and GeCl+4 in the range 11–26 eV. Vacuum UV radiation from a synchrotron source dispersed by a 5 m normal-incidence McPherson monochromator ionizes the parent molecule, and electrons and ions are detected by threshold electron analysis and time-of-flight mass spectrometry, respectively. Undispersed fluorescence from the interaction region can also be detected, allowing the three different types of coincidence experiment to be performed. The optimum resolution of the monochromator is matched to that of the threshold analyzer, and this work improves on preliminary results using a 1 m Seya monochromator [Chem. Phys. 174, 441 and 453 (1993)] where the resolution of the spectra was limited by that of the optical source. TPEPICO spectra are recorded continuously as a function of photon energy, allowing both threshold photoelectron spectra and yields of all the fragment ions to be obtained. Kinetic energy releases can also be measured at fixed photon energies with good time resolution. PIFCO and TPEFCO spectra are recorded at fixed photon energies. The former experiment can yield the fate of the lower electronic state of the parent ion to which fluorescence occurs. The latter experiment yields the lifetime of the fluorescing state; with sufficient resolution of the photoionizing radiation, the lifetime is specific to one vibrational level of the emitting electronic state. For CF+4 and SiF+4 work has concentrated on the third and fourth excited states, C̃ 2T2 and D̃ 2A1, of which only the C̃ state of SiF+4 does not decay radiatively. Vibrationally state-selected fluorescence quantum yields and lifetimes have been measured for four levels of the C̃ state of CF+4, and absolute values of radiative and nonradiative decay rates have been evaluated for these levels. Jahn–Teller distortion of the C̃ state of SiF+4 from Td to C3v geometry assists internal conversion of the C̃ 2T2 state into high vibrational levels of the B̃ 2E state, and is an efficient route for nonradiative decay. A non-Franck–Condon distribution of intensities is observed in the threshold photoelectron spectrum of the D̃ 2A1 state of CF+4, due to autoionization from a high-lying Rydberg state of neutral CF4. For the two chloride molecules, SiCl4 and GeCl4, fragmentation of the ground (X̃) and the first four excited states (ÖD̃) of the parent ion have been studied at slightly lower resolution. For SiCl+4 an important result is confirmation of the stability of its electronic ground state with respect to dissociation to SiCl+3+Cl. By contrast, a substantial part of the Franck–Condon zone of the ground state of GeCl+4 is energetically unstable with respect to GeCl+3+Cl. Radiative decay from the C̃ 2T2 state of both ions is an important process. The decay dynamics of all the valence states of this family of tetrahedral ions are reviewed. Dynamical, rather than statistical, processes generally dominate, and reasons for these surprising phenomena are discussed.

Nonradiative decay pathways of electronic states of group IV tetrafluoro and tetrachloro molecular ions studied with synchrotron radiation

The nonradiative decay channels of the valence electronic states of the gas-phase tetrahedral ions CF+4, SiF+4, CCl+4, SiCl+4, and GeCl+4 have been studied in the range 35–100 nm by a novel form of photoionization mass spectrometry. Tunable vacuum UV radiation from a synchrotron source ionizes the parent neutral molecule, and electrons and ions are detected by the photoelectron–photoion coincidence technique. The experiment is repeated continuously as a function of photon energy, and a three-dimensional histogram of photon energy versus ion time of flight versus coincidence count rate is produced. By taking cuts through this histogram, photoionization curves for the different fragment ions can be extracted. The appearance energies of the fragment ions (e.g., CF+2 from CF4, CCl+ from CCl4) occur at the adiabatic ionization potential of an electronic state of the parent ion, and not at the thermodynamic appearance energy of that ion. Attempts to measure the kinetic-energy releases in the fragmentation pathways have only been partially successful. The results are complementary to those of recent experiments to probe the radiative decay of these electronic states of MX+4 [M=C, Si, Ge; X=F, Cl] [J. Chem. Phys. 89, 2675 (1988); 89, 2683 (1988)], where the C̃ 2T2 and D̃ 2A1 third and fourth excited electronic states can show radiative decay to a surprising degree. The decay dynamics of the C̃ and D̃ states of MX+4 are reviewed. In general, the fluorides show different behavior to the analogous chlorides, and the carbon species behaves differently to the corresponding silicon or germanium species.

Ab initio calculations on the group IV tetrafluoride radical cations

The pseudo Jahn-Teller effect manifest in the group IV tetrafluoride radical ions CF 4 +., SiF 4 +. and GeF 4 +. was studied by ab initio methods including configuration interaction. Calculations were made up to the fourth excited state. These calculations show that higher states are stable and that the weak pseudo Jahn-Teller effect found in the C state of CF 4 +. increases in SiF 4 +. a GeF 4 +•. The molecules are found to dissociate in the X and in the A state. Ionisation potentials are calculated in good a with experiment.

Ab initio calculations on the dissociation of the CF 4+• radical ion

The dissociation of CF 4 +• was calculated by ab initio methods. Calculations were made up to the fourth excited state. The calculations show that CF 4 +• may dissociate in the ground state and dissociates in the first excited state to CF 3 + and a fluorine atom; higher excited states are stable. A weak pseudo Jahn-Teller effect is found in C state. Ionization potentials of CF 4 and the wavelength for the D → C transition of CF 4 +• were also calculated.

Spin-orbit splitting of the A2Π and D2Π states of BeF by ab initio MRD CI calculations

Abstract The electronic structure and energetics of the X 2 Σ + ground state and several excited states of beryllium-monofluoride have been investigated by means of the MRD CI method using a GTO DZP AO basis set. The potential curves are characterized by avoided crossings between bound ionic and repulsive covalent configurations leading to double minimum potentials in case of the second and fourth excited states, B 2 Σ + and D 2 Π. Concerning the first-order spin-orbit splitting of the A 2 Π state, the choice of one-particle functions is found to be essential for a proper description of the highly ionic charge distribution. Using parent natural orbitals the calculated spin-orbit splitting A 0 21.2 cm −1 is in excellent agreement with experiment results.